COVID-19 is, for the moment, in retreat, and public health measures are loosening accordingly: Every state has dropped or will soon end its mask mandate; major employers like Starbucks and major cities like Boston, Washington, D.C., and San Francisco are dropping vaccine requirements; countries around the world are reopening to travelers. But relaxing the measures that protect us against viral spread only makes sense if we can also be confident that less virus is spreading.
How do we gain this confidence? By getting ahead of the virus.
Throughout the pandemic, we've largely been playing catch-up. Much of what public health officials have been tracking—cases and deaths, for example—are lagging indicators, snapshots from the past, which are already out of date by the time the data is disseminated. The lag time that comes with such metrics means they are not the best indicators to inform public health policies meant to curb the spread of the fast-moving virus that causes COVID-19 and its many subvariants.
Far more useful are leading indicators—data that shows where the virus is headed, not where it has already been. One such data set comes from an unexpected and decidedly low-tech place: our wastewater.
Much of what public health officials have been tracking are lagging indicators, snapshots from the past, which are already out of date by the time the data is disseminated.Share on Twitter
Wastewater functions as a true community-level picture of near-real-time disease spread: The data stream is continually created, pooled, and anonymized. For years, medical experts have used wastewater to track the spread of diseases such as polio and norovirus. At the start of the pandemic, some municipalities began using the technique to track the level of COVID-19 viral material in their wastewater. Last fall, such tracking in major cities like Houston and New York allowed public health officials to detect the omicron variant as early as 11 days before anyone in the United States tested positive for the variant. That extra lead time is critical because it can allow public health officials to adjust their strategies to help prevent a surge. It's for that reason that counties like Santa Clara and Los Angeles, for example, have routinely monitored their sewage for coronavirus.
The Centers for Disease Control and Prevention recognized the value of wastewater surveillance early on and launched the National Wastewater Surveillance System in September 2020. The system is a coordinating tool for building the country's capacity to track coronavirus in wastewater samples. And while data from the system was recently added to the CDC's COVID Data Tracker, nationwide coverage from it is still quite sparse, with only “clusters” of sites in a handful of states, according to recent reporting.
Expanding the system might be a game changer for public health agencies across the United States, but the transition from lagging to leading indicator isn't always smooth.
In the early 2010s, excitement ran high about social media and other, similar “digital exhaust”—the wastewater equivalent of our online data. Google Flu Trends was a tool built to capitalize on web searches for flu-related symptoms. The idea was that patterns in those searches would predict clinical reporting of flu symptoms—someone searching Google for common flu symptoms, for example, might indicate that they or members of their household had the flu.
If it had worked, Google Flu Trends would have accurately shown where flu was spreading—a sea change that would have allowed health departments and hospitals to prepare for specific waves of disease well in advance. But Google Flu Trends was no better at predicting flu cases than the CDC's reporting, and it also failed a major test: It didn't see the H1N1 pandemic coming. It turned out that online behaviors, like social media posts or web searches, are, at best, indirect measures of the real world. As of 2015, Google Flu Trends was no longer being updated.
Fortunately, unlike web searches, wastewater is a leading indicator that is a direct measure of what's actually happening on the ground. There is also another key difference: While our digital data is mostly captured by and captive to private companies, our wastewater data is collected by government agencies that are by and large eager to make the data available for public benefit.
Wastewater functions as a true community-level picture of near-real-time disease spread.Share on Twitter
In order to realize the CDC's aims, the system will need more data from areas of the country not currently tracking their wastewater, metrics will need to be standardized so trends can be compared across communities over time and public health workers will need to be trained or provided guidance on how to use the metrics. Properly executed, this information would provide policymakers with specific and understandable indicators to inform when to reinstate or relax COVID-19 safety measures like mask mandates.
Building up the robustness of a surveillance system will take financial support. But it's not clear Congress will provide it. COVID-19 funding was recently pulled from a $1.5 trillion measure after Republicans and Democrats couldn't reach an agreement on where the funding would come from. While there is bipartisan support for the Prevent Pandemics Act that is working its way through Congress, the bill only includes an additional $2 billion in spending. A bipartisan group of health officials has called for allocating $10 billion to biodefense.
The National Wastewater Surveillance System has the potential to significantly change the way we fight not just COVID-19, but future pandemics and any other viruses or bacterial diseases that could be circulating in populations, too. Getting ahead of disease in this way is something of a holy grail for public health. And to think, it's just from the stuff we flush.
Douglas Yeung is a behavioral scientist at the nonprofit, nonpartisan RAND Corporation and a member of the Pardee RAND Graduate School faculty.
This commentary originally appeared on San Francisco Chronicle on March 23, 2022. Commentary gives RAND researchers a platform to convey insights based on their professional expertise and often on their peer-reviewed research and analysis.